Elevator cars in a multi-mobile elevator installation are typically each equipped with an own drive and an own braking system. The electronic control of the overall elevator installation is frequently so designed that no collisions of the individual elevator cars should occur. In particular, in the case of an emergency stop or even in the case of a normal storey stop of an elevator car it cannot be guaranteed in all circumstances that a further elevator car disposed above or below in the same elevator shaft can still stop at the correct time in order to avoid a collision. This could be avoided in that sufficient spacings between the individual elevator cars and also appropriately adapted vertical speeds were predetermined by the control. However, due to such presetting the transport capacity of a multi-mobile elevator installation cannot be fully utilized, which has an influence on the cost/utilization efficiency.
A multi-mobile elevator installation is known from European Patent Specification EP 769 469 B1, which comprises means for opening the safety circuit of an elevator installation if there is an undesired approach to another elevator car. According to the patent specification safety modules which evaluate the car positions and speeds so as, in a given case, to be able to trigger braking processes even at other elevator cars, are present at each elevator car. The individual safety modules must always recognize and evaluate the car positions and speeds of the other participating elevator cars in order to be able to correctly react in an emergency case. A specific decision module is needed for that purpose, which in the emergency case is responsible for determining the stop commands.
A similarly complicated solution is known from International Patent Application WO 2004/043841 A1. According to this patent application infrared, laser or ultrasound sensors are arranged at each elevator car and measure the spacings from the adjacent elevator cars disposed above and below the elevator car. Furthermore, it is additionally proposed to use a shaft information system so that, for example, measuring strips arranged in the shaft can be scanned by sensors at the elevator cars in the form of light barriers. This electro-optical approach also makes it possible to control the spacing of the elevator cars and in a given case also the spacing from the shaft bottom and if needed to intervene in the control in order to prevent a collision.
The solution described in International Patent Application WO 2004/043841 A1 is, above all, complicated, because it obliges a communication between different opto-electronic components of the elevator cars so as to enable statements about the instantaneous state and the instantaneous speeds of the elevator cars.
Moreover, the described solutions are complicated to initialize when placing in operation, since all systems have to be matched to one another. The complexity of the systems makes these solutions possibly also susceptible to fault.